Grading of Prostate Cancer: Past, Present, and Future.

The grading of prostate cancer has undergone significant changes since the adoption of the Gleason grading system in the 1970s. Gleason patterns 1 and 2 are no longer in use and the current Gleason score 6 of 10 is the lowest grade possible. Several specific morphologies that were historically considered Gleason grade 3 are currently assigned a Gleason pattern 4. Consequently, current Gleason score 6 cancers have a better prognosis than historic ones. There is now ample literature that supports that Gleason score 7 includes patients with very different prognosis; those with Gleason score 3 + 4 have a much better prognosis than patients with Gleason score 4 + 3. Within patients with high-grade cancer, it is now also clear that patients with Gleason score 8 have a significantly better prognosis than men with Gleason scores 9-10. Additionally, more recent studies have demonstrated that there is no significant difference in the prognosis of patients with Gleason score 9 or 10, making the distinction between the two pointless. A new contemporary grading system has been proposed that addresses these changes/problems and provides a simpler system with only five grades that reflect more accurately the prognosis of each group. We review the different changes applied to the Gleason scoring system since its conception as well as the studies leading to a new contemporary grading system.